Hot pressing process

ABSTRACT

AN IMPROVED PROCESS FOR HOT PRESSING MOLDED PULP ITEMS WHICH COMPRISES APPLYING AN AQUEOUS EMULSION OF SILICONE OIL TO MOISTEN A PORTION OF THE SURFACE OF A PULP MOLDED ITEM WHICH IS SUBSEQUENTLY HOT PRESSED. THE CONCENTRATION OF SILICONE IN THE EMULSION IS AT LEAST ABOUT 0.0025% BY WEIGHT. THE PROCESS REDUCES THE AMOUNT OF FOREIGN DEPOSIT BUILD-UP ON THE PRESS MOLDS NORMALLY ASSOCIATED WITH HOT PRESSING OPERATIONS.

United States Patent 01 Patented Aug. 1, 1972 lice ABSTRACT OF THEDISCLOSURE An improved process for hot pressing molded pulp items whichcomprises applying an aqueous emulsion of silicone oil to moisten aportion of the surface of a pulp molded item which is subsequently hotpressed. The concentration of silicone in the emulsion is at least about0.0025% by weight. The process reduces the amount of foreign depositbuild-up on the press molds normally associated with hot pressingoperations.

BACKGROUND OF THE INVENTION Field of the invention The invention relatesto improvements in the manufacture of molded pulp items and moreparticularly to the improvements of hot pressing operations by applyingto the surface of the molded pulp item, which is to undergo hotpressing, a dilute aqueous emulsion containing an additive prior topressing to thereby reduce sticking, buildup of foreign deposits on thefinished portion of the pressed mold, and reduce the shutdown timeassociated with the process as practiced in the prior art.

Description of the prior art The hot pressing operation as it iscustomarily practiced in the molded paper pulp industry, involves theformation and drying of molded pulp items by conventional processing andthereafter moistening a portion of the item on which a finished surfaceis desired with water, followed by passing the item through a hot pressin which one of the mold portions have heated smooth or shiny finish,which by virtue of the pressing or ironing operation, is imparted to themoistened portion of the molded pulp structure.

It is well known that molded pulp items have a generally rough surfacetexture which is not especially suitable for printing and furthermore,do not have the attractive smooth finish which the commercial andconsumer markets require for this type of product. For example, in thefield of molded pulp egg cartons, especially the type of carton known asa 2 x 6 egg carton, a container is provided which has cavities in thelower portion of the container for holding two rows of six eggs each.The cover for the container is connected to the bottom by means of anintegrally formed hinge and conventionally has a smooth top surfacehaving a substantial portion thereof planar and which is customarilyused for printing the name of the food packager.

The use of water alone as a moistening agent for those portions of themolded pulp carton or other items which undergo hot pressing, results insome transfer of deposits of foreign materials from the pulp item to thesmooth finished portion of the mold used in hot pressing operations. Thesmooth part of the mold is customarily made of metal, and is usuallychrome plated and highly polished. The non-finished portion of the moldused in this operation is frequently made of dissimilar materials, andsince it contacts a non-moistened portion of the carton, does notpresent any particular problem of build-up of foreign deposits which areassociated with the smooth portion of the mold. The deposits whichcontain alum, rosin, wax, and other additives, are the result of asolubilization of components of the pulp composition which then transferby virtue of the moisture from the pulp material to the mold surface.The foreign deposits as indicated above, result in sticking of themolded items in the hot press with consequent damage to the molded item,result in frequent shutdowns for cleaning, cause corrosion and produceimperfect surfaces. In the industry, it has not been uncommon to requirecleaning at three hour intervals with a consequent shutdown andsubstantial loss of production time.

SUMMARY OF THE INVENTION The present invention comprises an improvedprocess for hot pressing of molded pulp items which comprises applying adilute aqueous emulsion of a silicone oil to a portion of the roughformed surface of the pulp molded item, and thereafter hot pressing themoistened surface.

The concentration of the silicone oil in the aqueous emulsion rangesupwards from at least about 0.0025 by weight to 2%. Amounts above 2% canalso be used but no economic advantage is derived thereby. A preferredconcentration of the silicone oil in the aqueous emulsion is from about.0075% to about 1%.

The emulsion is applied to the portion of the carton or pulp molded unitby means of spraying of the item to moisten the surface, it beingunderstood that the portion of the surface to which the siliconeemulsion is applied is that which is intended to undergo the hotpressing operation. Other means such as roll coating or the like, canalso be used. The hot pressing occurs on a production basis generallyimmediately after the spraying, since the molded pulp items prior totreatment have been through the conventional drying operation. It isnecessary that the hot pressing occur while the moisture from thespraying remains on the pulp surface to achieve the desired ironing orsmoothing effect.

The amount of the silicone fluid deposited on the surface of the pulpmolded item to be hot pressed is not critical, however, it is preferredthat the same be applied at a rate of from about 0.003 to 0.100 ounceper 1,000 square feet.

The process of the invention is preferable to hot pressing operations inwhich the finish or pressed portion of the molded item is obtained bythe use of a highly finished or polished mold portion usually of chromeplated metal and having a smooth finish usually of polished chromium orsimilar alloy. The other portion of the mold used in the hot pressingoperation is usually of a material which does not have a surfacespecially prepared to produce a smooth finish on the pressed item.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The process of the presentinvention is most preferably applied to the hot pressing operation ofegg cartons, and more particularly, to the hot pressing of the coverportions of 2 x 6 molded pulp egg cartons. In the most preferred form,the silicone material used is a dimethyl siloxane, represented by thestructural formula:

wherein R and R are selected from the group consisting of aryl and loweralkyl. The lower alkyl groups preferably contain up to about 4 carbonatoms and methyl is the most preferred. The polymeric silicone material,of course, can be of variable molecular weight, but generally speaking,the integer n may have values from 83 to 2100 to produce siliconeshaving viscosities of above about 50 centistokes and preferably from10,000 to 100,000 centistokes. The characteristics of the silicone oilpolymer notwithstanding the particular substituents which are employedin the silicone polymer precursor are desirably such as to provide afilm which (a) is capable of wetting the metal in the mold to form acontinuous relatively adherent film; (b) will withstand the heat andpressure conditions encountered during hot pressing operations; will begenerally physically inert with respect to the dies and die surfaces;and (d) will not adversely effect the printability of the carton cover.

Conventionally, the emulsion is prepared using a nonionic emulsified,such as for example, trimethyl nonyl polyethylene glycol ethers whichare sold under the trade name of Tergitol TMN (Union Carbide) orpolyoxyethylene lauryl ethers sold under the trade names BRIJ 30 and 35(Atlas Chemical). The following specific example will illustratespecific embodiments of the process of the present invention.

EXAMPLE An aqueous silicone oil emulsion having the trade designation LE463, manufactured by Union Carbide, was diluted with from its original35% concentration to a concentration of 0.346%. This dilute silicone oilemulsion was conveyed by means of mixing pumps and blended with water toproduce a silicone emulsion spray at the spray head having a siliconeoil concentration of about 0.0075

A fine spray of the diluted silicone emulsion was applied in a manner soas to moisten the total cover portion and the hinge area of a 2 x 6molded pulp egg carton which was then passed through the hot pressingoperation wherein the cover was hot pressed in a mold; the femaleportion of said mold was formed of chrome plated metal and the maleportion of plastic. The following tables will illustrate the run time,the amount of time down for cleaning, and the percentage of productiontime lost for cleaning. For comparison purposes, a conventional waterspray technique wherein water was sprayed on the carton surfaces insteadof silicone is also shown.

TABLE II.HOT PRESS TRIALS-RUN NO. 2

Silicone Conditions spray Water spray Term of observation 30 hrs..." 29hrs. 30 mins. No. of die c1eanings 9 Total time required for clear tinNon Percent production time loss for cleaning," 0. 00 7. 45

From the foregoing examples, it is readily apparent that the use ofsilicone oil emulsions on a treatment of molded pulp items in hotpressing operations results in very substantial savings in down timerequired for cleaning as compared to conventional hot pressingoperations using water as the moistening agent. In the comparative runsdescribed in Tables I and II above, the percentage of production timelost for cleaning in the water spray process is substantial. It shouldalso be noted that in the runs of Table 11 using the silicone sprayprocess, the cleaning of the mold surface did not require wire brushingbut only water spray, indicating that the deposits formed were onlylightly adhered to the mold surface.

What is claimed is:

1. An improved process for hot pressing the outer surface of a driedmolded pulp container having a rough surface texture to provide a smoothprintable surface thereon, said container having a substantially planarsurface thereon, which comprises moistening a rough formed surface ofthe molded pulp container by spraying of an aqueous emulsion of siliconepolymer oil having a strucwherein R and R are selected from the groupconsisting of aryl and lower alkyl containing up to about 4 carbon atomsand n having a value from 83 to 2100 on said surface, wherein theemulsion has a silicone polymer concentration of at least 0.025%, saidsilicone polymer having a viscosity of from about to about 100,000centistokes, said emulsion being applied to the surface at a rate offrom about 0.003 to 0.100 ounce of silicone polymer solids per 1000square feet; and hot pressing the moistened portion in a die to impart asmooth surface thereto.

2. A process according to claim 1, wherein the emulsion has a siliconeoil concentration of from about 0.0075 to about 1% by weight.

3. A process according to claim 1, wherein the silicone is a dimethylpolysiloxane.

References Cited UNITED STATES PATENTS 3,014,833 12/1961 Lee 11764 R2,819,184 1/1958 Smith et al. 11764 R 2,950,502 8/1960 Weaver 11764 R3,505,097 4/1970 Ratcliffe 11764 R 2,745,233 5/1956 Collings et a1.ll7-l39.5 A 3,190,791 6/1965 Potter 162-224 3,373,079 3/1968 Eastman eta1 162-224 3,468,755 9/1969 Culp 16 --224 WILLIAM D. MARTIN, PrimaryExaminer 5 W. R. TRENOR, Assistant Examiner US. Cl. X.R.

11764 C, 65.2, 139.5 A, R; 162-224

